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Ferrite core

The Nixdorf SM 8890 keyboard contains a type of moving-magnet Ferrite core switch that may have been designed and manufactured by Nixdorf. The switches represent an alternative approach to miniaturisation compared to the switches in Cortron’s FC-2550 and FC2500 keyboards. As with some other Cortron types, the plunger assembly is separate from the ferrite core assembly and can be removed from the keyboard by itself. In the Nixdorf arrangement, the ferrite core and its drive and sense loops are held in assembly that is soldered to the PCB. An adjacent aperture in the PCB allows the plunger and the magnet it contains to move down past the PCB and clear of the ferrite core.

There is a a second model in this family with the same switches.

A search for a patent for these switches has not yielded any results.


To computer keyboard enthusiasts, the term “Nixie” refers not to numeric indicators, but a custom variation of the Cherry MX switch with a colourless translucent cover. These switches are specific to certain Nixdorf keyboards (e.g. Nixdorf CT11), hence their moniker. The reason for this specific variation remains a mystery; MX designer Günter Murmann has no recollection of it or of any reason why it would have been created.